SESSION 3

Mention common rapid antibody test used in detecting diseases

Explain the underlying principles of antibody rapid test

Identify the sample for antibody rapid tests

Perform HIV rapid testing according to guidelines and procedures

Perform Syphilis rapid testing according to guidelines and procedures

Interpret the result of rapid antibody test

LEARNING OBJECTIVES

Serum is a fluid obtained from coagulated blood

Antibody

A protein that is produced by the immune system as a result of stimulation by antigen.

Window period

The time delay between infection and the development of antibodies.

Definition of terms

Syphilis rapid test

Malaria rapid test.

Hepatitis B rapid test

Hepatitis C rapid test

Covid 19 Rapid test

common rapid antibody test used in detecting diseases

Firstly a small of blood, serum or plasma is collected from the patient. Then the rapid test device contains antigens that are specific to the pathogen being tested for, these antigen are usually protein or other molecules found on the surface of the infectious agent.

Thirdly if an individual has been infected the body’s immune system produce antibodies. In the test kit any antibody present in sample will bind to the antigen on the device.

Then it will produce a sign for the antigen-antibody reaction line will appear on the device or strip.

Finally interpretation of results after the specific time, test results are interpreted based on the presence or the absence of the strip line. If any antibodies detected it indicates positive result and If no any antibodies detected indicates negative results

HIV rapid test is an immunochromatographic technique which is used to detect HIV antibodies in blood. Specimens for this technique include whole blood, serum and plasma.

When performing HIV rapid test three blood samples must be available; known HIV positive sample, known HIV negative sample and a sample of unknown HIV status.

HIV Rapid Tests Used (Currently) in Tanzania

SD Bioline HIV-1/2

Unigold HIV

Antibody methods (to detect HIV)

HIV Rapid tests

Enzyme Linked Immunosorbent Assay (ELISA)

Western Blot (confirmatory test if available)

DNA PCR tests

Useful in infant (<18 months) diagnosis

The national protocol for PCR outlines the details of PCR testing

PCR can only be done at well-equipped laboratories at referral hospitals

Principle of the test

The test is based on antibody and antigen reaction, interpretation is based on manufacturers manual

Antibody + Antigen = Agglutination which is detected as a colour change on the respective test (Reactive/ Positive result)

No Antibody + Antigen = No agglutination (no colours change) (Non Reactive / Negative result)

They can’t determine Sero-status during window period

On some occasions some individuals take longer to develop antibodies. (During that time HIV rapid tests will be negative but DNA/RNA PCR will demonstrate presence of the virus)

Before performing the test the tester should record/indicate/have the following information;

The test date

Client identification

Name of the person performing the test

The name of the test

The expiration date of the test kit

Test lot and batch number of the test kit

A standard operating procedure

Results slip and register

National (Serial) Testing Algorithm

An algorithm is a process, set of rules, or ‘step-by-step procedure for reaching a clinical decision or diagnosis, often set out in the form of a flow chart, in which the answer to each question determines the next question to be asked

Figure below shows the different possible test outcomes for an HIV test, using the national algorithm. The gray boxes mean that the test does need to be performed. If the test results are reactive, they must be confirmed by another test. If the test is non-reactive (for Bioline), the test does not need to be repeated.

Materials and Supplies

It is important to be prepared with all the supplies and materials that are needed for HIV testing. These include:

Gloves

Aprons or laboratory coats

Timer, clock, or wrist watch with minute hand

Transfer pipettes, pipette tips

HIV rapid testing kits

Alcohol

Cotton Gauze / wool

Sterile lancets and syringes

Safety box/ sharps bin or disinfectant jar for lancets

Marker pen for marking or labelling

Paper towels for bench coating, cleaning, and hand washing

Antiseptic for hand washing

Leak-proof bag for containing or moving labelled biohazard waste for incineration

Disinfectant e.g. Jik, Clorox

Bandages or plasters

Finger-prick sample is recommended but if not tested in the room, venous blood samples should be drawn carefully and slowly and sent to the lab as quickly as possible. Stored in the refrigerator and NOT frozen.

Sample tube should be labelled with

Patient identification number

Collection date

Finger pricks should be done on the side of the finger, not in the middle. The ring finger is the preferred finger for pricking because it has a large surface area. Finger preparation for collecting blood through a finger prick involves the following steps:

Position hand palm-side up. Choose the ring finger, or whichever finger is least calloused

Apply intermittent pressure to the finger to help the blood to flow

Clean the fingertip with alcohol. Start in the middle and work outward to prevent contaminating the area. Allow the area to dry

Hold the finger and firmly place a new sterile lancet off-centre on the fingertip

Firmly press the lancet to puncture the fingertip

Wipe away the first drop of blood with a sterile gauze pad or cotton ball

Collect the specimen. Blood may flow best if the finger is held lower than the elbow

Apply a gauze pad or cotton ball to the puncture site until the bleeding stops

SD Bioline HIV Rapid Test

Materials Required

Bioline HIV1/2 KIT

Standard operating procedure

Gloves

Aprons or laboratory coats

Timer, clock, or wrist watch with minute hand

Alcohol

Cotton Gauze / wool

Sterile lancets and syringes

Safety box/ sharps bin or disinfectant jar for lancets

Marker pen for marking or labelling

Paper towels for bench coating, cleaning, and hand washing

Antiseptic for hand washing

Leak-proof bag for containing or moving labelled biohazard waste for incineration

Disinfectant e.g. Jik, Clorox

Bandages or plasters

Register book

Serum, plasma or whole blood is used

Pipette required amount of specimen and add to the device well (10μl for serum or plasma,20μl for whole blood)

Add three drops of essay diluent

Wait for 15 to 20 minutes

Read the results

Uni-Gold HIV Test

Materials required

Uni-Gold HIV1/2 KIT

Standard operating procedure

Gloves

Aprons or laboratory coats

Timer, clock, or wrist watch with minute hand

Alcohol

Cotton Gauze / wool

Sterile lancets and syringes

Safety box/ sharps bin or disinfectant jar for lancets

Marker pen for marking or labelling

Paper towels for bench coating, cleaning, and hand washing

Antiseptic for hand washing

Leak-proof bag for containing or moving labelled biohazard waste for incineration

Disinfectant e.g. Jik, Clorox

Bandages or plasters

Register book

Collect test items and other necessary laboratory supplies

Remove device from package and label device with client identification number

Collect specimen using the disposable pipette

Add two drops (approx. 60μl) of specimen to the sample port in the device

Add two drops (approx. 60μl) of the appropriate wash reagent to sample port

Wait for 10 minutes (no longer than 20 min.) before reading the results

Read and record the results and other pertinent information on the worksheet

Quality control (QC): Comprises measures for verifying that a test is working. The measures are taken in order to monitor the validity of the technical aspects of the test procedure. QC includes the testing of samples with known results so as to verify that the testing procedure and materials are working properly

Internal

Onsite audit

On-site audit is necessary in order to confirm that all SOPs are adhered to, including QC, record-keeping and observation of staff performance.

A programme of on-site auditing should include a standard checklist of testing service indicators.

Proficiency testing

Proficiency testing (PT) or EQA schemes involve the distribution of small panels of samples with known results to all testing sites.

External

Blinded rechecking

Accomplished by forwarding 5%-10% positive and 5%−10% of negative specimens for retesting at a higher level laboratory (reference laboratory)

RPR it means (rapid plasma reagin) while VDRL(venereal disease research laboratory) are the screening test for syphilis, it measure antibodies presence or absence in the sample of a patient with suspected infection.

Purpose

A syphilis test is used to detect antibodies present in serum or plasma in patients with a syphilis infection.

Principle

The test is used to detect reagin (non-specific) antibodies present in serum or plasma in patients with a syphilis infection.

Purpose and principle of the rapid tests for syphilis (RPR and VDRL)

The antigen is a modified RPR/VDRL antigen bound to microparticulate carbon, which enhances the visual detection of aggregation in the presence of reagin antibodies.

If reagin antibodies are absent, no aggregation takes place.

Purpose and principle of the rapid tests for syphilis (RPR and VDRL) cont…

VDRL/RPR KIT

Standard operating procedure

Gloves

Aprons or laboratory coats

Timer, clock, or wrist watch with minute hand

Alcohol

Cotton Gauze / wool

Sterile lancets and syringes

Disposal bucket

Reagents, materials, equipment and types of sample

Whole blood from EDTA sample or finger prick, or Plasma, serum is the specimen of choice, depending on the manufacturer’s instructions for the type of kit used.

Reagents, materials, equipment and types of sample cont…

Take the required number of test strips or devices, allowing sufficient for controls.

Procedure

Label the strips/devices with the number for each sample and control (positive and negative) to be tested.

Carefully follow the instructions in the kit insert for performing the tests.

Validate and interpret the results.

Record the results in a worksheet.

Place all strips/devices, used droppers and other materials in the bucket marked “INCINERATION”

Procedure cont….

Indicate date and name of technical staff reporting.

REPORTING RESULTS cont…..

During interpretation of result, after report

Positive result write due/ because of two strip or red band appeared, one in the test line and in control line.

While Negative results is due to the appearance of one line to the control line.

Define rapid antibody test

Mention common rapid antibody test used in detecting diseases

Explain the underlying principles of antibody rapid test

Identify the sample for antibody rapid tests

Perform the rapid antibodies test and interpret the results